Drilling invert arcuate paths beneath obstacles such as rivers and ocean inlets or bays and bayous is known. Representative of such drilling are the disclosures of my earlier patents entitled Apparatus and Method for Emplacing a Conduit Along An Underground Arcuate Path U.S. Pat. No. 3,894,402 issued Jul. 15, 1975; Drilling and Installation System U.S. Pat. No. 4,121,673 issued Oct. 24, 1978; and, Drilling Method and Apparatus for Large Diameter Pipe U.S. Pat. No. 4,221,503. Additionally, the readers attention is directed to the Article 30-Inch Line Bored Under Green's Bayou is “On Target” from the March, 1978 Pipeline & Gas Journal. The disclosures of these documents is incorporated by reference herein as if set forth in full.
Summarizing the state of the art evidenced by these publications, a pre-bent large diameter pipe was inserted along an invert arcuate path under a water body, such as a bayou. A hydraulic powered drill head had a separate drilling rig connected hydraulic circuit to power the drill head. Similarly, a plurality of separate drill rig connected hydraulic circuits were used to articulate the drill head with respect to the pipe; typically one circuit was required for each degree of movement of the drill head. Additionally, a separate hydraulic circuit was used to drive a mud evacuation pump to evacuate under pressure cuttings from the drill head to the pipe entry point. Finally, a pressurized annulus was required about the large diameter casing. In the case of Green's Bayou, this annulus was provided with a special (and expensive) pressurized mud mixture that both “floated” the installed conduit and provided the require lubricity necessary for casing installation.
In the case of Green's bayou, it should be noted, that the pressure on the annulus was in excess of ambient fluid pressure on the path along which the drilled conduit was disposed. Drilling was from ground level on one side of the bayou to ground level on the opposite side of the Bayou.
Modern Problems Encountered
Of recent date, drilling has been required to enter the ocean. Where fiber optic cables are being laid, drilling through and out beyond the surf zone has been required. Otherwise, the action of the surf and sand rapidly abrades away the conventional armor placed around fiber optic cables.
Once one is beyond the surf zone, an area of the ocean is entered that can be called the maritime zone. In the maritime zone, ground tackle from ships such as chains and anchors are hazards to the installed cable. The most expedient solution is to trench cable to a depth of several meters through such maritime zones.
In the usual case, for each fiber optic cable laid, a separate conduit is drilled. The separate drilled conduit provides a protective barrier against the conventional abrasion in the surf zone. Once the cable is out beyond the surf zone, trenching techniques are used to bury the cable through the maritime zone. Thereafter, cable is conventionally laid on the ocean bottom surface.
Often, a single entry point is utilized for cables headed to many destinations. By way of example, optical fibers entering through a single pit ashore can individually be destined for widely differing destinations. A single shore entry point on the Pacific Coast of the United States could serve to accommodate optical cables destined for Hawaii, China, Formosa, Japan, Indonesia, and the like. The result, when viewed in plan, is a fan like array of individual drill strings originating at a common point on shore and extending out into the ocean beyond the surf zone and into the maritime zone. Thereafter, trenching of the cables occurs through the maritime zone.
The “trenching” of installed cable from the end of such drilled conduits is known. In such trenching techniques, a diver removes the drill head from the single drilled pipe. An optical fiber cable is then threaded to the conduit end. Thereafter, cable is laid using an under ocean bottom trenching apparatus. Such trenching apparatus buries cable in the ocean floor up to a depth of several meters. When the cable is conventionally buried, nautical ground tackle—such as anchors and their attached chains—have a reduced chance of harming the installed cable.
Of late, environmental concerns have effected such drilling through surf zones. Specifically, drilling mud leaking from the drilled annulus around the drilled pipe or “string” into the ocean environment has become a concern. It is believed that conventional drilling utilizing drilling mud constitutes an environmental hazard in the ocean in the ecologically sensitive surf and maritime zones.
Contributing to this environmental concern is the typical formation geology encountered along such surf and maritime zones. Since these zones are in the usual case active sites for wave—induced erosion and land—sea shore geologic activity, the formations are frequently fractured. These fractures provide paths along which drilling mud can escape.
Another environmental concern is where large diameter pipes are drilled underneath a water body for relatively long distances. When drilling long distances, the ambient pressure in drilling mud required for powering the drilling apparatus at the leading edge of the pipe being placed exceeds both the hydrostatic pressure and the ability of the geologic formation to resist leakage. In such cases, drilling mud can escape into the water body producing significant pollution.
In the usual drilling operation, drilling mud is introduced under some pressure at the drill head and channeled by conduit to the cutting bit at the leading end of the drill. The cutting bit is usually powered. For example, a mud powered Moyno motor can be used to drive a cutting bit.
When cutting occurs, mud and drill tailings escape along an annulus between the outside of the drilled casing and the soil surrounding the bore. The path of the mud in the annulus is from the cutting head of the drill bit back to the on-shore entry pit where initial introduction of the drill string occurred. In order to assure evacuation of the drilling mud and cuttings, pressure is applied to the transporting drilling mud flowing from the drill head to the entry pit. In order to assure mudflow, this pressure can exceed the ambient hydrostatic pressure of the ocean and surrounding soil and ocean water. The pressure required to assure mudflow is in large measure a function of the distance the mud must travel in the annulus about the pipe and in the geologic formation.
Remembering that the drill string is traversing eroded and geologically active zones, paths are present for drilling mud under pressure to escape. As a result, drilling mud frequently leaks into the ocean from the annulus surrounding such individually drilled conduits. Alternately, the pressure of the mud can exceed the ability of the formation and hydrostatic pressure to contain the mud. Leakage into the ambient body of water above the drilling can result. Lakes and rivers can be polluted.
In what follows, I introduce a concept for solving the above-enumerated problems. In so far as the prior art has not specifically enumerated the problems set forth above, invention is claimed. It goes without saying that recognition of the problem to be solved can constitute invention.